From the prior art hybrid drive trains for motor vehicles are known, which comprise an internal combustion engine and an electric machine with a rotor and a stator. In addition the known hybrid drive trains comprise a transmission usually in the form of an automatic transmission, and the internal combustion engine can be connected releasably to the input shaft of the transmission by means of a clutch whereas the rotor of the electric machine is connected to the input shaft of the transmission.
For example, DE 103 46640 A1 by the present applicant describes a drive train for a hybrid vehicle, in which an internal combustion engine is in driving connection with a separator clutch whose output side is connected to a transmission input shaft which is connected to an input element of the automatic transmission. In this known drive train the transmission input shaft can also be driven by an electric machine and for that purpose the rotor of the electric machine is connected to the transmission input shaft.
DE 10012221 A1 describes a hybrid drive train in which an internal combustion engine is in driving connection with a separator clutch whose output side is connected to a transmission input shaft itself connected to an input element of an automatic transmission, whereas the rotor of an electric machine is connected to the transmission input shaft via a transmission input stage with a high gear ratio; this brings the advantage that the electric machine can be made smaller since the rotational speed level of the electric machine is decoupled from that of the internal combustion engine and by virtue of the gear ratio, sufficient torque is available for purely electric driving.
It is particularly advantageous for the separator clutch between the internal combustion engine and the transmission input shaft to be a disk clutch whose outer disk carrier is connected rotationally fixed to the planetary carrier of a planetary transmission unit which serves as the transmission input stage and whose inner disk carrier is connected to the internal combustion engine, whereas the rotor of the electric machine drives the ring gear of the planetary transmission unit and the sun gear of the planetary transmission unit is coupled to the housing.
In such transmissions the unit comprising the electric machine, the separator clutch and the transmission input stage also fulfills the functions of a hydrodynamic converter.